We are pleased to share that we have added a normalization option in the Registry as a part of our API 3.0 work. This allows identifiers which are case insensitive, such as DOIs, to be processed as the same regardless of case on the ORCID record. Therefore, they are grouped as expected. You can find the card with the update on our current development Trello, or view your ORCID record for an example if this issue has affected you previously: https://trello.com/c/5p6QK7bS/4254

Let us know if you find case sensitive identifiers which are not grouping on your record as expected.